Exocytosis of neurotransmitters, hormones and other cell secretory products is believed to occur by calcium-dependent movement of the secretory vesicle to the cell surface and subsequent fusion of the secretory vesicles with the plasma membrane. We have discovered a calcium-sensitive linkage of secretory vesicles to the cytoskeletal protein actin. We have found that the calcium binding protein synexin binds the inside of the plasma membrane as well as the secretory vesicle membrane. Membranes drawn together by this protein were demonstrated to fuse together when exposed to arachidonic acid at concentrations comparable to those present in stimulated cells. Working with isolated adrenal medullary cells we have found that epinephrine secretion appears to depend upon an energy dependent chemiosmotic lysis of the secretory vesicle.